A consideration of the reduction of blood platelets in purpura

Abstract

As is well known, typical purpura is characterized by a marked diminution in the number of platelets; whereas the normal individual has about 300,000 platelets per cubic centimeter of blood, the purpuric individual has less than 100,000. Evidently this abnormal condition may be due either to a lack of formation of these cells, or to their increased destruction. A number of studies have been undertaken to decide this question, but no conclusive evidence has been brought forward.

The coagulation time of the plasma centrifugalized for fifteen minutes is normal in purpura or but slightly prolonged. If we centrifugalize plasma for two hours we find that, whereas the coagulation time in the normal case has been greatly prolonged—for example—from 8 to 18 minutes (Case 1, Table I), in the case of purpura, the centrifugation has frequently occasioned but little or no delay in coagulation (see Table I). This distinction may be interpreted as due to the fact that in the normal plasma we have removed all the platelet cells, whereas in the purpuric plasma, there is considerable platelet substance in solution which could not be removed by means of centrifugation.

This question can also be answered by means of employing a dilute solution of hirudin, an antithrombic substance, which combines with thromboplastic substances such as platelets. If we remove practically all the suspended platelet cells by means of prolonged centrifugation, we shall then be able to determine whether or not there is platelet substance in solution by attempting to neutralize it by the addition of hirudin. This test has been carried out in many normal as well as purpura cases. It has been found that whereas the addition of the hirudin solution to the centrifugalized normal plasma brings about considerable delay (in Case 3 of the table, from 8 to 30 minutes), in the purpuric plasma on the contrary, a considerably less degree of retardation is effected (for example, in Case 7-from 11 to 16 minutes).